Torrefied biomass briquettes and related methods

ABSTRACT

The presently disclosed subject matter relates to torrefied biomass briquettes and methods for producing the same that make use of a mixture of lightly torrefied material (LTM) and highly torrefied material (HTM) and/or make use of torrefied materials that are subjected to a hydrolysis pretreatment prior to being torrefied.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/771,795, filed Jun. 11, 2020, incorporated herein by reference in itsentirety, which is a U.S. national phase patent application filed under35 U.S.C. Section 371 based on PCT International Patent Application No.PCT/US2018/065145, filed Dec. 12, 2018, incorporated herein by referencein its entirety, which is based on and claims priority to United Statesof America Provisional Patent Application Ser. No. 62/597,542, filedDec. 12, 2017, the disclosure of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The presently disclosed subject matter generally relates to torrefiedbiomass densification and related methods. In particular, certainembodiments of the presently disclosed subject matter relate totorrefied biomass briquettes and methods for producing the same thatmake use of a mixture of lightly torrefied material (LTM) and highlytorrefied material (HTM) and/or make use of torrefied materials that aresubjected to a hydrolysis pretreatment prior to being torrefied.

BACKGROUND

Coal has historically been the staple fuel for power generation in theUnited States due to its abundance, high heating value, and relativelylow processing costs. Until recently, approximately 40% of all powergenerated in the United States was produced by coal and the recentdecline has been attributed to the lowering cost of natural gas andenvironmental regulations. These regulations have typically been stricton coal due to its chemical composition and tendency to release harmfulproducts into the environment including sulfur, mercury, NOx, SOx, andgreenhouse gases (CO, CO₂, and the like). These and the particulatematter released from coal smoke have been detrimental to the health ofhuman and animal populations in areas by instigating high levels of smogand ultrafine particulate matter. Mining also negatively impacts thehealth of those involved with its processing. Black lung disease, amongother respiratory complications, has lowered the average life expectancyin coal miners due to the constant exposure to coal dust and miningconditions. Mining is also a leading contributor to environmentaldestruction, causing soil erosion and ecosystem damage that preventsplants and animals from prospering in affected areas even when the minesare sealed. In order to help combat the detrimental effects of coal,alternatives must be found that ensure a secure and healthy energyfuture.

Instead of a positive net carbon production, carbon dioxide resultingfrom burning biomass is taken back in by the plants that are cultivatedfor future use as fuel. Using biomass also eliminates sulfur and mercuryexposure due to the lack of said chemicals in plant matter. However,energy density of biomass compared to that of coal is considerablylower, approximately 37 MJ/kg for anthracite coal to 17-21 MJ/kg forbiomass (on a dry basis). This results in larger, and thereforecostlier, power plant operations. Biomass also tends to have a lowphysical density and high moisture content, making the volumes needed topower homes and cities increase dramatically compared to that of coal.Movement of these large volumes from farm to power plant creates aneconomic disadvantage as transportation costs increase proportionallywith said volume increases. In addition, power plants would need to bere-tooled to effectively burn the biomass as grinding efficiency of thematerial, durability of the fibers, and the tendency of biomass to holdonto water all impact the heating value and processing methods. Inaddition, biomass can contain ash that can lead to scaling and isproblematic in combustion units in a power generation plant.

Thus, biomass is a renewable fuel that has the potential to play asignificant role as a source of renewable energy. However, its usage islimited due to poor characteristics of low energy density and lowhydrophobicity that creates problems especially in handling and storageas compared to coal, which is still the dominant solid fuel inelectricity and heat generation. Technologies (such as biomasstorrefaction) have thus been investigated to pre-treat or upgradebiomass, in an effort to overcome its limitations and raise itspotential as a substitute to coal.

After torrefaction, the biomass loses its binding ability. Hence, achallenge of torrefaction is to be able to maintain the binding abilityfor densification of the torrefied biomass. Densification of torrefiedbiomass into briquettes would help reduce the challenges associated withshipping, storage and handling at coal fired power plants. Currently,the densification typically requires the use of an external binder tomake the briquettes hydrophobic, durable and transportable. However, thebinders and the associated infrastructure for the binders addsignificantly to the production costs of torrefied briquettes. Hence,there is a need to eliminate the use of binders such that the productioncost of briquettes is reduced while maintaining the hydrophobicity,durability and transportability of the briquettes. There is also a needto enhance the overall economic viability of using torrefied biomass toproduce a coal alternative.

SUMMARY

This summary lists several embodiments of the presently disclosedsubject matter, and in many cases lists variations and permutations ofthese embodiments. This summary is merely exemplary of the numerous andvaried embodiments. Mention of one or more representative features of agiven embodiment is likewise exemplary. Such an embodiment can typicallyexist with or without the feature(s) mentioned; likewise, those featurescan be applied to other embodiments of the presently disclosed subjectmatter, whether listed in this summary or not. To avoid excessiverepetition, this Summary does not list or suggest all possiblecombinations of such features.

A torrefied biomass briquette is provided in accordance with thepresently disclosed subject matter. In some embodiments, the torrefiedbiomass briquette comprises: (a) about 10% to about 95% of ahighly-torrefied material (HTM) and about 5% to about 90% of a lightlytorrefied material (LTM); (b) a torrefied acid hydrolyzed biomass havinga FTIR profile comprising one or more reduced oxygen functionalities ascompared to biomass not subjected to acid hydrolysis; or (c) acombination of (a) and (b). In some embodiments, prior to densification,the HTM and the LTM have a combined moisture content of about 7% toabout 15%. In some embodiments, subsequent to densification, thebriquette has a moisture content of about 3% to about 10%.

In some embodiments, the briquette exhibits lignin based in-situ bindingand is free of an added binder. In some embodiments, the briquette has adensity in the range of about 1 to about 1.5 gm/cm³. In someembodiments, the briquette has a durability index value of about 5% tomore than about 93%. In some embodiments, the hydrophobicity of thebriquette is increased relative to a briquette including only LTM. Insome embodiments, the briquette has a calorific value of about 8,000BTU/lb to about 10,000 BTU/lb.

A method of producing a torrefied biomass briquette is provided inaccordance with the presently disclosed subject matter. In someembodiments the method comprises producing a mixture comprising about10% to about 95% of a highly-torrefied material (HTM) and about 5% toabout 90% of a lightly torrefied material (LTM); preheating the mixtureto a predetermined temperature; and compressing and simultaneouslyheating the mixture. In some embodiments, prior to the compressing andheating, the HTM and the LTM have a combined moisture content of about7% to about 15%. In some embodiments, subsequent to the compressing andheating, the briquette has a moisture content of about 3% to about 10%.

In some embodiments, the mixture is pre-heated to a temperature of about40° C. to about 80° C. In some embodiments, the method further comprisesadjusting the moisture content of the mixture prior to compression. Insome embodiments, heating the mixture comprises heating the mixture in adie to a temperature of about 200° C. to about 250° C. In someembodiments, the mixture does not include a binder. In some embodiments,the LTM and/or the HTM of the mixture is formed by providing a biomass;and subjecting that biomass to an acid hydrolysis.

In some embodiments, a torrefied biomass briquette produced by themethod is provided.

A method of producing a torrefied biomass is provided in accordance withthe presently disclosed subject matter. In some embodiments, the methodcomprises: providing an amount of a biomass; subjecting the biomass toan acid hydrolysis to produce a hydrolyzed biomass; and torrefying thehydrolyzed biomass. In some embodiments, the biomass comprises wood.

In some embodiments, the method further comprises drying the biomassprior to torrefying the hydrolyzed biomass.

In some embodiments, a portion of the hydrolyzed biomass is subjected totorrefaction at a temperature ranging from about 160° C. to about 220°C. and/or a portion of the hydrolyzed material is torrefied attemperatures above about 240° C.

In some embodiments, the method further comprises compressing thehydrolyzed biomass; and simultaneously heating the hydrolyzed biomass ata predetermined temperature to form a torrefied biomass briquette.

In some embodiments, a torrefied biomass produced by the method isprovided. In some embodiments, a torrefied biomass briquette produced bythe method is provided.

Thus, it is an object of the presently disclosed subject matter toprovide torrefied biomass briquettes and related methods.

An object of the presently disclosed subject matter having been statedhereinabove, and which is achieved in whole or in part by the presentlydisclosed subject matter, other objects will become evident as thedescription proceeds when taken in connection with the accompanyingFigures as best described herein below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a die (diameter in mm) used in representativeapproaches for making briquettes in accordance with the presentlydisclosed subject matter. The used die configurations are(42-36)(36-36)(36-36)(36-40) and (42-34)(34-34)(34-34)(34-40).

FIG. 2 is a graph showing bulk density versus moisture content ofbriquettes produced in accordance with the presently disclosed subjectmatter.

FIG. 3 is a graph showing a linear correlation between mechanicaldurability and bulk density.

FIG. 4 is a graph showing Fourier-transform infrared spectroscopy (FTIR)spectrums of the densified biomass samples.

FIG. 5 is a graph showing a FTIR analysis for hydrolyzed and torrefiedwood.

FIG. 6 is a graph showing a thermo-gravimetric analysis (TGA) combustioncurve for hydrolyzed wood.

DETAILED DESCRIPTION

The details of one or more embodiments of the presently-disclosedsubject matter are set forth in this document. Modifications toembodiments described in this document, and other embodiments, will beevident to those of ordinary skill in the art after a study of theinformation provided in this document. The information provided in thisdocument, and particularly the specific details of the describedexemplary embodiments, is provided primarily for clearness ofunderstanding and no unnecessary limitations are to be understood therefrom. In case of conflict, the specification of this document, includingdefinitions, will control.

While the terms used herein are believed to be well understood by thoseof ordinary skill in the art, certain definitions are set forth tofacilitate explanation of the presently-disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart to which the invention(s) belong.

All patents, patent applications, published applications andpublications, databases, websites and other published materials referredto throughout the entire disclosure herein, unless noted otherwise, areincorporated by reference in their entirety.

Where reference is made to a URL or other such identifier or address, itunderstood that such identifiers can change and particular informationon the internet can come and go, but equivalent information can be foundby searching the internet. Reference thereto evidences the availabilityand public dissemination of such information.

As used herein, the abbreviations for any protective groups, amino acidsand other compounds, are, unless indicated otherwise, in accord withtheir common usage, recognized abbreviations, or the IUPAC-IUBCommission on Biochemical Nomenclature (see, Biochem. (1972)11(9):1726-1732).

Although any methods, devices, and materials similar or equivalent tothose described herein can be used in the practice or testing of thepresently-disclosed subject matter, representative methods, devices, andmaterials are described herein.

The present application can “comprise” (open ended), “consist of”(closed), or “consist essentially of” the components of the presentinvention as well as other ingredients or elements described herein. Asused herein, “comprising” is open ended and means the elements recited,or their equivalent in structure or function, plus any other element orelements which are not recited. The terms “having” and “including” arealso to be construed as open ended unless the context suggestsotherwise.

Following long-standing patent law convention, the terms “a”, “an”, and“the” refer to “one or more” when used in this application, includingthe claims. Thus, for example, reference to “a cell” includes aplurality of such cells, and so forth.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as reaction conditions, and so forth usedin the specification and claims are to be understood as being modifiedin all instances by the term “about”. Accordingly, unless indicated tothe contrary, the numerical parameters set forth in this specificationand claims are approximations that can vary depending upon the desiredproperties sought to be obtained by the presently-disclosed subjectmatter.

As used herein, the term “about,” when referring to a value or to anamount of mass, weight, time, volume, concentration or percentage ismeant to encompass variations of in some embodiments ±20%, in someembodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, insome embodiments ±0.5%, and in some embodiments ±0.1% from the specifiedamount, as such variations are appropriate to perform the disclosedmethod.

As used herein, ranges can be expressed as from “about” one particularvalue, and/or to “about” another particular value. It is also understoodthat there are a number of values disclosed herein, and that each valueis also herein disclosed as “about” that particular value in addition tothe value itself. For example, if the value “10” is disclosed, then“about 10” is also disclosed. It is also understood that each unitbetween two particular units are also disclosed. For example, if 10 and15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

As used herein, “optional” or “optionally” means that the subsequentlydescribed event or circumstance does or does not occur and that thedescription includes instances where said event or circumstance occursand instances where it does not. For example, an optionally variantportion means that the portion is variant or non-variant.

I. General Considerations

Biomass includes the waste materials of agriculture, forestry, anddifferent other sources, which have low-value and limited use with highdisposal costs. But, biomass is the fuel that has the potential to playa significant role as a source of renewable energy. Instead of apositive net carbon production, carbon dioxide resulting from burningbiomass is taken back in by the plants that are cultivated for futureuse as fuel. But, usage of biomass is limited due to poorcharacteristics of low energy density, durability (handling andtransportation), hydrophobicity, storage, and others.

An objective has been to develop a “drop-in” biomass derived coal thatperforms similar to coal and can be integrated in to the existing coalinfrastructure of the coal fired power plants either replacing orsubstituting for coal. While this kind of bio-coal production is anatural fit from an environmental and health standpoint, the economicsbehind it still cannot overcome the cost-effectiveness of coal. Onemajor road block to the implementation of biomass derived coal is itshigh cost compared to traditional coal. Depending on the cost ofbiomass, the production cost of biomass derived coal ranges between$200-$250 per ton (compared to $50-$80 per ton of coal). Currently,woody biomass with about 50% moisture content costs approximately$80/MT. It therefore presents economic challenges for this bio-coal tobe used at current prices (even with carbon credits) for powergeneration. Taking advantage of compounds in the biomass structurebefore torrefaction could help improve economics by creating co-productsthat could provide additional profit to mitigate the higher productioncosts. Hemicellulose is a large component of most biomass species and isdestroyed in the torrefaction process. Hemicellulose can be extractedand recovered as high-value xylose in large quantities at a fairlyminimum monetary and energy cost.

Torrefaction is a thermal treatment process carried out in a chemicallyinert environment to improve hydrophobicity and energy content ofbiomass. The resulting product appears as energy densified brown toblack solid, and the characteristics obtained after torrefaction candepend on process conditions, such as temperature, time of torrefaction,and type of feedstock as well as the type of torrefaction equipmentemployed. At high or severe torrefaction, the energy density of the fuelis increased to a great extent.

Several challenges arise after torrefaction of biomass materials, suchas poor density and high amount of dust formation during handling. Thesechallenges need to be addressed for the commercial use of torrefiedmaterial. In order to make use of torrefied biomass commercially, thematerial should be densified. Densification is the process of compactionof torrefied materials or biomass residues into a product of higherdensity than the original raw material. Such a conversion has manypotential advantages, including increasing calorific value per unitvolume, increasing convenience of transportation and storage, reducingdust emissions, solving the problem of residue disposal, and making auniform final product.

A challenge associated with the densification of torrefied biomass isthe difficulty of getting a desirable quality (i.e., through density anddurability) in densifying biomass particles after they have beentorrefied. A reason is due to the chemical changes that happen to thebiomass components, such as lignin, after torrefaction. Duringtorrefaction (200-300° C.), lignin undergoes reactions ofdepolymerisation, demethoxylation, bond cleavage, and condensation,while hemicellulose will decompose and both will have an amount ofreduction with the dehydration of the biomass. Hemicellulose isresponsible for the existence of hydrogen bonding sites. Lignin mainlycan produce covalent bonding when activated. These chemical changes playa role in not getting good binding leading to poor densification and inlow durability for the torrefied biomass.

II. Compositions and Methods

In some embodiments, the presently disclosed subject matter employstorrefaction and densification of biomass to create a coal substitute.This torrefaction and densification process provides severalimprovements to the biomass that address at least in part the issuesdiscussed elsewhere herein. After torrefaction and densification,biomass product has higher calorific value and is hydrophobic anddurable. Torrefaction helps to remove oxygenated functionalities ofligno-cellulose structure of the biomass, carbonizing it and creating amore hydrophobic and more energy dense material. This provides heatingvalues closer to coal and allows storage without the fear of rotting ordegradation. These characteristics subsequently aid in effectivetransportation of the resulting torrefied material. Torrefactionprovides brittleness as well, allowing for torrefied material to be moreeasily ground and used in current coal plant infrastructures.

A challenge associated with the densification of torrefied biomass isthe difficulty in getting the desirable binding, density and durabilityin densifying biomass particles after they have been torrefied. In someembodiments, the presently disclosed subject matter provides approachesfor densifying a mixture of highly and lightly torrefied biomass withthe object of using that lightly torrefied material as the main sourceof binding by enhancing their inherent natural lignin.

Torrefied biomass represents a high quality renewable energy source.Torrefaction pretreatment can be generally classified into light, mild,and high corresponding to temperatures of approximately 200-235° C.,235-275° C., and 275-300° C., respectively. Densification of torrefiedbiomass (for example, into briquettes) improves the logistics associatedwith bulk transportation, handling, and storage for heat and powerapplications. Two primary deliverables from densification are durabilityand hydrophobicity of the briquettes. The use of external binders andwaxes to promote these attributes can be prohibitively expensive.

Hence, the utilization of lignin in-situ of the biomass to promotebinding and hydrophobicity is provided in accordance with someembodiments of the presently disclosed subject matter. Lignin, across-linked thermoplastic polymer, tends to break down and lose itsbinding ability after the high temperature torrefaction of the biomass.In this regard, the presently disclosed subject matter is based, atleast in part, on the development of an approach that utilizes a mixtureof biomass torrefied at two different temperatures, such that onebiomass component delivers native lignin for binding and the otherdelivers high carbon content for BTU content. The biomass deliveringlignin—a lightly torrefied material LTM—is torrefied at a lowertemperature range (160-220° C.) while the other biomass component—ahighly torrefied material HTM—is torrefied at temperatures above 240° C.This mixture can then be densified, such as by using a ram typebriquetter. The utilization of LTM to deliver thermally modified lignin(as opposed to using untorrefied biomass that can only deliverunmodified lignin) can help maintain the hydrophobicity and BTU value ofthe densified and torrefied material. In some embodiments, and asdescribed further below, the particle size of the binder (LTM), mixturemoisture content, temperature of the mixture, the ratio of LTM to HTM,and die configuration in the briquetter are modulated to deliverhydrophobic and highly durable briquettes with energy densities in therange of 8,000-10,000 BTU/lb.

The presently disclosed subject matter includes torrefied biomassbriquettes and methods of forming such briquettes. In some embodiments,a torrefied biomass briquette is provided that comprises about 10% toabout 95% of a highly-torrefied material (HTM) and about 5% to about 90%of a lightly torrefied material (LTM). In some embodiments, a torrefiedbiomass briquette is provided that comprises about 10%, about 20%, about30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%,or about 95% of a HTM. In some embodiments, a torrefied biomassbriquette is provided that comprises about 5%, about 10%, about 20%,about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, orabout 90% of a LTM.

In some embodiments, the briquette has a FTIR profile comprising one ormore reduced oxygen functionalities. In some embodiments, the briquettecomprises a torrefied biomass and/or an acid hydrolyzed biomass (asbinder) having a FTIR profile comprising one or more reduced oxygenfunctionalities as compared to biomass not subjected to acid hydrolysis.In some embodiments, the briquette exhibits lignin based in-situ bindingand is free of an added binder. The in-situ lignin is provided to theHTM and LTM mixture through the LTM and/or is also provided through theacid hydrolyzed biomass. The briquetting method described in accordancewith the presently disclosed subject matter allows the in-situ lignin tobe entrained by the generated steam, distribute through the structure ofthe briquette, and promote bonding within the briquette.

The term “briquette” is used herein to refer to blocks of compressedbiomass of the presently disclosed subject matter that are of a suitablesize and shape for use as a fuel source. In this regard, the term“briquette” is typically used to refer to blocks having dimensions inthe range of less than about 1 cm (and including 1 cm) to about 10 cm,but can be further inclusive of blocks having smaller or greaterdimensions. In some embodiments, the term “briquette” is inclusive oftorrefied pellets and the like as would be recognized by those skilledin the art.

With respect to the biomass utilized in accordance with the presentlydisclosed subject matter, the term “biomass” as used herein is used torefer to fuel derived from organic matter, including plant and animalmatter. For example, in some embodiments of the presently disclosedsubject matter, the biomass is wood. As another example, in someembodiments, the biomass is an agricultural biomass or, in other words,a biomass that is derived from agricultural sources including, but notlimited to soy hulls from soybean processing, rice hulls from ricemilling, corn fiber from wet milling or dry milling, bagasse fromsugarcane processing, pulp from sugar beets processing, distillersgrains, and the like.

In some embodiments, the presently disclosed subject matter provides amethod of producing a torrefied biomass briquette. In some embodiments,the method comprises producing a mixture including about 10% to about95% of a highly-torrefied material (HTM) and about 5% to about 90% of alightly torrefied material (LTM); adjusting the moisture of the mixture,preheating the mixture to a predetermined temperature, and compressingand simultaneously heating the mixture.

Regardless of the particular source of biomass, and as indicated above,to produce a torrefied biomass briquette in accordance with someembodiments of the presently disclosed subject matter, a mixture of LTMand HTM is first produced and provided in which the HTM is in an amountof about 10% to about 95% and the LTM is an amount of about 5% to about90%. In such a mixture, the materials comprising the LTM have previouslyundergone torrefaction at a lower temperature range (e.g., about 160° C.to about 220° C.), while the HTM has been torrefied at temperaturesabove about 240° C. In this regard, once combined, the LTM is configuredto provide thermally-modified lignin for binding the briquette togetherand the HTM provides a material with an energy content higher than thatfound in the LTM and capable of providing an increased BTU value uponburning. In some embodiments, the method comprises an initial step ofproviding a biomass, such as those biomasses described above, and thensubjecting that biomass to an acid hydrolysis as described herein belowprior to treatment.

Upon mixing the LTM with the HTM in a desired ratio, such as thosementioned above, the moisture content of the mixture can be adjusted toa desired level. In some embodiments, the moisture content can beadjusted with the addition of water or steam. In some embodiments, byadjusting the moisture content of the starting material, a briquette cansubsequently be produced having a desired durability, density, and orhydrophobicity, as described in further detail below. In someembodiments, prior to compressing the mixture while heating as describedbelow, the HTM and the LTM mixture has a combined moisture content ofabout 7% to about 15%, such as, in some embodiments, a moisture contentof about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about11%, about 12%, about 13%, about 14%, about 15%. In some embodiments,the moisture content is about 8% to about 14%. Compressing the mixturecan also be referred to as densifying the material or as densificationof the material.

Subsequent to adjusting the moisture content, the mixture of HTM and LTMmaterials are then typically preheated to a temperature of about 40° C.to about 80° C. (e.g., about 50° C. by steam) before being fed into adie system where the materials in the mixture undergo compression whileheating for a period of time to simulate a hydrothermal torrefactionduring compression and heating of the biomass. The preheating can occurat a temperature of about 40° C., 45° C., 50° C., 55° C., 60° C., 65°C., 70° C., 75° C., or 80° C. By way of example not limitation, themethod can comprise compressing the mixture at temperatures of about200° C. to about 250° C. (e.g., about 200° C., 205° C., 210° C., 215°C., 220° C., 225° C., 230° C. 235° C., 240° C., 245° C., or 250° C.) toproduce a briquette. In some embodiments, subsequent to the compressingwhile heating aspects of the procedure, the resulting briquettes have amoisture content of about 3% to about 10% after densification,including, in some embodiments, a moisture content of about 3%, about4%, about 5%, about 6%, about 7%, about 8%, about 9%, or about 10%.

Through the simulated torrefaction during densification of a materialincluding a mixture of LTM and HTM and by utilizing the adjustedmoisture contents indicated above, in some embodiments, a torrefiedproduct or material is produced having improved properties relative tomaterials produced with HTM or LTM alone or relative to other availabletorrefied biomass materials or products. For instance, in someembodiments, by making use of such materials and processes, a briquetteis produced without the use of binder (i.e., a binding agent) that istypically required to produce torrefied biomass briquette of sufficientquality. In some embodiments, the resulting briquette has an increase indensity, a durability index value of about 50% to more than about 93%,an increase in hydrophobicity relative to briquette including only LTM,and/or a calorific value of about 8,000 BTU/lb to about 10,000 BTU/lb,including about 9,000 BTU/lb.

In some embodiments, the briquette has a density in the range of about 1to about 1.5 gm/cm³, including a density of about 1.053 gm/cm³, about1.1 gm/cm³, about 1.2 gm/cm³, about 1.213 gm/cm³, about 1.3 gm/cm³,about 1.4 gm/cm³, or about 1.5 gm/cm³. In some embodiments, thebriquette has a durability index value of about 5% to more than about93%, including about 10%, about 20%, about 30%, about 40%, about 50%,about 60%, about 70%, about 80% and about 90%.

Thus, in some embodiments, the presently disclosed subject matterprovides native lignin in the form of lightly torrefied material (LTM)and also provides for the modifying of the lignin in-situ such that theresulting briquette is hydrophobic as well as durable. The presentlydisclosed subject matter provides combinations of materials, equipment,and processes to produce durable and transportable torrefied briquetteswithout the use of an added binder. In some embodiments, the presentlydisclosed subject matter employs ratios of wood torrefied at a lower(Lightly torrefied material—LTM) and higher (highly torrefiedmaterial—HTM) temperature. In some embodiments, a LTM and HTM, at arepresentative range of particle size, such as might be provided byusing a screen or sieve having pore sizes ranging from 1/16 inch or lessto 1 inch or less, are mixed to a representative ratio of moisture(typically 7-15%), such as with the addition of water or steam. In someembodiments, this material is preheated to about 40-80° C. and sent tothe feeding hopper of the briquetter for densification. Representativescreen/sieves sizes thus include 1/16 inch or less, ⅛ inch or less, ¼inch or less, ½ inch or less, ¾ inch or less, and 1 inch or less

Any suitable die configuration as would be apparent to one of ordinaryskill in the art can be employed in accordance with the presentlydisclosed subject matter. In some embodiments, the die configuration onthe briquetter includes a conical die, 1-3 extension dies (to controlretention time), and an end die. As would be apparent to one of ordinaryskill upon a review of the instant disclosure, retention times can varydepending on the production rate and biomass type. By way of example andnot limitation, the retention time can vary between 2 to severalseconds, with a preference for longer retention times, but typically notin minutes. In adding more retention dies, impact on machine runnabilityis considered. Additionally, in some embodiments, the die configurationcan include an extension die with a cooling jacket in order to flashcool the briquette. Representative die configurations are(42-36)(36-36)(36-36)(36-40) and (42-34)(34-34)(34-34)(34-40). See, forexample, FIG. 1.

In some embodiments, the die configuration is preheated prior to theintroduction of the feed mixture. In some embodiments, the dieconfiguration is preheated to 200 to 250° C. prior to the introductionof the feed mixture. In some embodiments, the pressure is maintained inthe range of 10,000 to 15,000 psi. Temperature, pressure, and moistureconditions present in the die, as well as that of feed mix, achieve thelignin modification to provide hydrophobicity and binding ability to thefeed mix. In some embodiments, the operating temperature of the dieconfiguration is at least about 200° C. to about 250° C. In someembodiments, the combination of the material mix and the dieconfiguration at the representative moisture content promoteshydrothermal treatment of the LTM and its lignin content and thegenerated steam allows for the flow of lignin within the briquettestructure, thus promoting hydrophobicity and durability through improvedbonding.

In some embodiments, the presently disclosed subject matter providesimproved product attributes and economic viability of a biomasstorrefaction plant. By way of elaboration and not limitation, hydrolysisbased C5 sugar extraction is gaining recognition as a method of valueaddition for industrial and agricultural biomass wastes. Additionally,coal substitution using torrefied biomass is deemed a viable alternativethat can develop around existing coal infrastructure. In accordance withthe presently disclosed subject matter, integrated hydrolysis based C5extraction and subsequent residual torrefaction are provided as anapproach to enhance feasibility of biomass to bio-coal. The presentlydisclosed subject matter demonstrates that hydrolysis increased theporosity of wood and this facilitated torrefaction in improvinghydrophobicity and energy content of wood by enhancing heat and masstransfer during torrefaction while reducing ash and air emissions. Insome embodiments, the presently disclosed subject matter demonstratesthat hydrolysis based C5 extraction of wood can be employed as apretreatment strategy that provides significant value addition as C5platform sugars, in addition to providing quality improvement forbiomass derived coal.

Thus, further provided, in some embodiments of the presently disclosedsubject matter, are pretreatment methods performed prior to producing atorrefied biomass to provide a torrefied biomass product having improvedproperties, where the methods make use of a hydrolysis procedure priorto torrefaction to produce an improved torrefied biomass product. Insome embodiments, a method of producing a torrefied biomass is providedthat comprises an initial step of providing a biomass, such as thosebiomasses described above, and then subjecting that biomass to an acidhydrolysis prior to torrefaction. For example, in some embodiments ofthe presently disclosed subject matter, to produce a sufficient biomasshydrolyzate, an amount of solid biomass material is initially placed ina reactor and is then exposed to an acid solution that is percolatedthrough the material at an elevated temperature and for a sufficientamount of time to allow a hydrolysis reaction to occur. In someembodiments, the elevated temperatures used in accordance with thehydrolysis procedure range from about 100° C. to about 150° C. (e.g.,about 100° C., 105° C., 110° C., 115° C., 120° C., 125° C., 130° C. 135°C., 140° C., 145° C., or 150° C.) with a reaction time of about 30 toabout 120 minutes (e.g., about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75,80, 85, 90, 95, 100, 105, 110, 115 or 120 minutes). Of course, a numberof acids can be used to effectuate a sufficient hydrolysis reactionincluding, in some embodiments, mineral acids such as sulfuric,hydrochloric, etc., and organic acids such as dicarboxylic acids (e.g.,oxalic, maleic, etc.) In some embodiments, the acid can be provided at aconcentration of about 0.2 wt % to about 5.0 wt %, including about 0.2,0.5, 0.7, 1.0, 1.2, 1.5, 1.7, 2.0, 2.2, 2.5, 2.7, 3.0, 3.2, 3.5, 3.7,4.0, 4.2, 4.5, 4.7, or 5.0 wt %. For further explanation and guidancerelating to reaction conditions for producing a biomass hydrolyzate,see, e.g., Fonseca, et al., Biomass and Bioenergy, 21 (2014), 178-186,herein incorporated herein by reference in its entirety. The hydrolysisreaction is a mild acid hydrolysis and the process conditions employedpromote selective hydrolysis of hemicellulose (C5) based sugars such asxylose and arabinose rather than hydrolyzing cellulose (C6) based sugar.Representative processes are also disclosed in Published U.S. PatentApplication No. 2016-0297845 and U.S. Pat. No. 10,093,953, hereinincorporated by reference in their entireties.

In some embodiments, subsequent to forming the hydrolyzate, the residualbiomass is then dewatered or dried to produce a hydrolyzed materialhaving desired moisture content in the range of 6 to 20%, includingabout 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%,about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about19%, and about 20%. Torrefaction is then performed according to methodsknown to those in the art and/or as disclosed elsewhere herein, wherebythe prehydrolyzed biomass is subjected to elevated temperatures (e.g.,300° C.) for a sufficient period of time (e.g., 30 min). Torrefactiontreatment can be classified into light, mild, and high corresponding totemperatures of approximately 200-235° C., 235-275° C., and 275-300° C.,respectively. In some embodiments, by subjecting a biomass to ahydrolysis pretreatment procedure, a torrefied biomass material orproduct can be produced having increased hydrophobicity, reduced sootand ash content upon burning, as well as an increase in calorific valuesas compared to torrefied materials produced using an unhydrolyzedbiomass.

In some embodiments, a portion of the hydrolyzed material is subjectedto torrefaction at a lower temperature range (e.g., about 160° C. toabout 220° C.) to produce a LTM. Further, a portion of the hydrolyzedmaterial is torrefied at temperatures above about 240° C. to produce aHTM. The LTM and HTM are then combined and treated in accordance withembodiments of the presently disclosed subject matter as disclosedherein above.

The presently disclosed subject matter is further illustrated by thefollowing particular but non-limiting Examples.

III. Examples Materials and Methods for Example 1-7

Production of Briquettes. The torrefied materials used in the studydescribed below were softwood and were sourced from Solvay BiomassEnergy, Quitman, Miss., United States of America. The initial moisturecontent was measured using Denver Instrument IR60 moisture analyzer(Denver Instrument Company, Bohemia, N.Y., United States of America) byusing a 1 gm sample. The moisture content was 8.20% for lightlytorrefied materials (LTM) while it was 6.76% for highly torrefiedmaterials (HTM).

The briquettes were produced using a C.F. Nielsen BPU 3200 commercialbriquetter (C.F. Nielsen, Baelum, Denmark). The LTM material was loadedby a screw feeder and processed at room temperature. The mixture of HTMand LTM materials were mixed in a 20:80 weight ratio and their moisturecontent was adjusted as shown in Table 1. The mixture was preheated toabout 50° C. using steam in a hopper. The die system in the briquetterwas made from alloy steel and had three extensions with the main die.Different conical orifice angles for the main die and end extension wereused. The results reported here were obtained using a die configurationwith a 36 mm inner diameter and also with a die configuration with a 34mm inner diameter. The die configuration was preheated to 250° C. andthe material was fed from the main hopper through a dosing screw to thecompression screw chamber at 10% of the rated feed capacity (rotating atabout 20 rpm). The operating temperature of the die was 225° C. for the36 mm die. During production, the temperature of the material at thecompression chamber was about 75° C. The produced briquettes wereallowed to cool to room temperature. The production rate of allbriquettes was about 130-140 Kg/hr, and the final moisture content inall briquettes varied from 3% to 7%.

By way of elaboration, the LTM material was loaded by a screw feeder andprocessed at room temperature to be the control samples. The mixture ofHTM and LTM materials are preheated to about 50° C. by placing them in ahopper containing a copper tube that is connected to a steam boiler. Thedie used in the machine is made from alloy steel and has threeextensions with the main die. Two die configurations were used, 36 mmand 34 mm inner diameter. The materials and feed moisture content usedin this study for each die set are shown in Table 1. The die waspreheated to 250° C. and the material was fed from the main hopperthrough a dosing screw to the compression screw chamber at 10% feed ratespeed, which is about 20 rpm. Then, the material was fed to thecompression chamber by the compression screw. The operating temperatureof the die was 225° C. for the 36 mm die and 240° C. for the 34 mm die.During production, the temperature at the compression chamber was about75° C. The mixture was softened and deformed in the main die by theaction of moisture, heat and pressure altogether. The producedbriquettes were allowed to cool to room temperature. The production rateof all briquettes was about 130-140 Kg/hr, and the final moisturecontent in all briquettes was 3-7%.

FIG. 1 shows a schematic of the die, the angles used for the conicalmain die, and the last extension. A coolant extension die was alsodesigned and made to be used to cool the briquettes in order to freezeany moisture and lignin before leaving the die. The effect of moistureon the briquettes shape indicates that the higher moisture gives darkerand shiny briquette (i.e. hydrothermal treatment effect).

TABLE 1 Materials Used and Associated Moisture Contents. Moisturecontent (%) Material 36 mm die 34 mm die 1 LTM 8.2 8.2 2 20% HTM-80% LTM10.75 7.5 3 20% HTM-80% LTM 14 10 4 20% HTM-80% LTM 16 12.79

Briquette Characterization. Bulk density was calculated by using thewater displacement method in which a small puck sample of each briquettewas taken after about 2 weeks of storage then weighed and coated withparaffin wax to prevent any water absorption during immersion in water.The waxed samples were weighed and then submerged into water. The volumeof the displaced water was measured and recorded as the volume of thewaxed sample. The volume of each sample was calculated by subtractingthe volume of coating wax from the volume of waxed samples. The bulkdensity of briquettes was calculated by dividing the weight of eachsample by the volume.

Hydrophobicity by moisture uptake was measured using a Fisher ScientificHumidity Chamber device (Fisher Scientific, Pittsburgh, Pa., UnitedStates of America). The briquette samples were first weighed then placedin the humidity chamber and maintained in 90% humidity at 30° C. for 24hours. The samples were then weighed and dried in an oven at 60° C. for6 hours, and final weights were recorded. The change in weight referredto moisture absorption.

A water immersion test was also conducted using two different times, 30second and 30 minute, to measure the water gain of each sample. Also, awater immersion test for 24 hours was conducted to observe the effect oflong time direct water contact on the produced briquette's shape.

The Durability Index of produced briquettes was determined according tothe ASAE S269.4 and ISO 15210 standards. The mechanical durability ofbriquettes were tested by specific abrasion drum (Gamet AutomaticSampling Equipment Company, Brooklyn Park, Minn., United States ofAmerica), in which samples of 500±50 g were weighed to the nearest 0.1 gand placed in the tumbling box device. Then they tumbled at 50±2 rpm for500 rotations. Then the samples were removed and passed manually througha 3.15 mm sieve. The mechanical durability index (DU) was calculatedusing the following formula:

DU=(M _(A) /M _(E))*100  (1)

Where: M_(E) is the mass of the samples before the drum treatment andM_(A) is the mass of sample left after sieving the resultant piecesafter tumbling.

The calorific value of the prepared briquettes was measured using a bombcalorimeter type IKA C2000 (IKA, Wilmington, N.C., United States ofAmerica). The device was calibrated using benzoic tablets of 1 gm andsample pieces of around 1 gm were used from each briquette for calorificvalue analysis.

The chemical functional groups that were present in briquettes wereanalyzed using FTIR spectroscopy using powdered samples of about 20 mgfrom each briquette. FTIR curves obtained were normalized to C═C peak at1506 cm⁻¹ assuming negligible change in aromatic ring count (originatedfrom lignin) in the sample.

Example 1 Characterization of Briquettes

Tables 2A and 2B show the characterization results for the producedbriquettes. As shown in the Table 2B, the briquette with 20% HTM and10.75% moisture performed better than the other samples in the 36 mmdiameter die. They showed a higher durability of 68%. They also showedthe lowest water gain after 30 seconds as well as after 30 minutes.

TABLE 2A Results of Briquettes Characterization 36 mm Diameter Die 34 mmDiameter Die 20% 20% Material LTM HTM-LTM LTM HTM-LTM Property (8.2% MC)(10.75% MC) (8.2% MC) (7.5% MC) Diameter (mm) 38 38 36.5 36.5 BulkDensity 1.178 1.065 1.191 1.213 (gm/cm³) Moisture 6.31 6.44 4.97 3.74content of produced briquettes (%) Moisture 8.23 8.66 8.77 8.07uptake(%) Water gain after 7.2 3.8 1.95 1.36 30 sec test immersion (%)69.8 30.5 30.43 30 30 min. test Durability 44.6 68 78.2 78.2 Index (%)Calorific value 9103 9369 9272 9659 BTU/lb (Kj/Kg) (21173.578)(21792.294) (21566.672) (22466.834)

TABLE 2B Characterization Results for Briquettes Produced from 36 mmDiameter Die Set 20% 20% 20% Material LTM HTM-LTM HTM-LTM HTM-LTMProperty (8.2% MC) (10.75% MC) (14% MC) (16% MC) Diameter (mm) 38 3838.5 38.5 Bulk Density 1.178 1.065 1.06 1.053 (gm/cm³) Moisture content6.31 6.44 7.2 7.8 of produced briquettes (%) Moisture uptake 8.23 8.667.91 7.26 (%) Water gain after 7.2 3.8 13 37.5 30 sec. test immersion(%) 69.8 30.5 47.6 63.3 30 min. test Durability Index 44.6 68 52.5 40.6(%) Calorific value: 9103 9369 9385 9459 BTU/lb (Kj/Kg) 21173.6 21792.321829.5 22001.6

Example 2 Effect of HTM Material and Moisture Content on Briquette Shapeand Binding

As shown in Tables 2A and 2B, the briquette made with 100% LTM showed ahigh level of moisture uptake and also has a lower energy contentcompared to the ones with HTM added at 20%. The addition of HTM not onlyimproved the energy content of the briquette, but also helped improvethe hydrophobicity. High moisture content can increase binding inbiomass material by activating (softening) the natural binders withinthat material such as lignin. Lignin is a thermoplastic material whichwould undergo plastic deformation at pressures and temperatures in therange of their glass transition temperatures. Also, high moisturecontent in the biomass along with the application of pressure andtemperature, a hydrothermal treatment can be made to the biomass whichactivates the natural binders while deforming the particles. Hence,maintaining a certain level of moisture content during densificationpromotes binding within the briquette. However, as shown in Table 2B,for moisture content above 10.75%, there was a reduction in thedurability of the briquette. When increasing the moisture content above10.75%, the briquettes appeared darker and showed hydrothermal impact;but the high moisture and the resulting steam formation duringdensification led to a significant number of cracks and this divided thebriquettes into small pucks. The diameter measurement results shown inTable 2B showed that briquettes had expanded compared to the innerdiameter of the die. The LTM briquettes had expanded about 2 mm whilethe mixed briquettes with higher moisture expanded a little more than 2mm. These cracks picked up more water as shown by water gain after 30sec and 30 minutes during the water immersion tests (Table 2B).

Example 3 Bulk Density

Bulk density is an important characteristic of biomass briquettes due toits influence on the handling and transportation of materials. As shownin Table 2B, bulk density decreased with the addition of HTM materialand with the increase of moisture content. This was due to the lightweight of HTM when compared to the LTM. Since high moisture combinedwith high temperature and pressure increases binding in biomass, densityshould also increase with the increase of moisture. However, thedecreased bulk density values in the mix HTM-LTM briquettes is due tothe resulting cracks and initial moisture content in the raw or mixmaterials. The lower bulk density values at higher moisture areexplained in detail (shown) in FIG. 2, in which the bulk densitydecreased with increasing of moisture content in the tested puck samplestaken from the produced briquettes for both die sets. The 7.5% moisturebriquettes produced using the 34 mm die showed the highest bulk density;this was evidenced by more compaction, higher binding and lower cracks.Also, the bulk density of 34 mm die briquettes was higher than that ofthe 36 mm for the same LTM material due to higher compaction resultingfrom lower die diameter. See Table 2A.

Example 4 Hydrophobicity

Briquette exposure to humid or rainy environments during transportationand storage could adversely affect the durability of the densifiedproducts; hence hydrophobicity of the briquettes is highly desired. Forthe water immersion results, feed moisture above 14% led to increasedwater uptake. Since this test used direct contact of water, it dependedmore on how densified the sample was and how many cracks were in it. At30 seconds time, the mix briquette with 10.75% moisture gave the lowestwater uptake followed by LTM briquette. Increasing the immersion time to30 minutes still showed that 10.75% sample have the lowest uptake, whilethe LTM sample absorbed more water than all of the mixed briquettes andeventually disintegrated. Further, 10.75% and 14% samples stayed intactat the end of this test. The 24 hours water immersion test results forthe 36 mm die set revealed that moisture content of 10.75% led toincreased water resistance and the sample stayed solid and intact aftertaking it out from water. In fact, the sample of 10.75% stayed intactafter 10 days of soaking. The one with 16% moisture could break upeasily when touched. Although higher moisture content can give thesebriquettes some binding with enhanced hydrothermal treatment, it did nothelp in binding the whole briquettes together along the die.

This could be mainly due to increased cracks in the briquettes duringthe release of excess moisture as steam and made small pucks in thebriquettes. The die temperature required for hydrothermal treatment wasalso reduced from 250° C. to 175° C. due to the presence of excessivemoisture. Same results were found for the 34 mm die briquettes exceptthat the cracks start at moisture content higher than 10%.

Example 5 Durability

Mechanical durability is one of the significant parameters from theviewpoint of handling and transportation using existing coalinfrastructure. The durability index results of each sample are shown inTables 2A and 2B. In Tables 2A and 2B, the highest durability index wasfor the 10.75% mix sample. Those low moisture levels reduced the cracksand enhanced overall binding (i.e. mechanical binding) compared to othersamples. FIG. 3 shows a plot of the measured mechanical durabilityvalues versus the calculated bulk density values and illustrates aninteresting correlation between durability index and bulk density of thebriquettes. The R-square values obtained near to 1, indicates that goodlinear correlation exists between the bulk density and mechanicaldurability of briquettes. The results of 34 mm die set in Table 2Afollowed similar behavior and these trends indicated that goodcompaction with better density provided strong durable briquettes.However, the lower durability index in the 36 mm LTM compared to 34 mmLTM may refer to lower in-situ binding even though it had higher densitythan 34 mm LTM sample. This could be due to the higher pressuresassociated with the 34 mm die in the briquetting process. It was clearthat adding of HTM material reduced the binding ability and this couldbe overcome by adopting optimized material and process parameters suchas moisture, pressures, and temperatures. In this study, good conditionswere provided by the 34 mm die, 7.5% moisture in the feed and dietemperature of 250° C.

Example 6 Heating Value

According to Tables 2A and 2B, higher calorific value always related tothe use of highly torrefied materials (HTM). Effective binding withoptimized balance of moisture content, process parameters and LTM/HTMmix gave briquettes higher heating value. On the other hand, highermoisture content helped in raising the heating value by promotinghydrothermal cooking; even though durability suffered from crackscreated from steam.

Example 7 FTIR

According to FIG. 4, increasing the moisture content in the feed reducedthe oxygen bearing functional groups such as O—H (3350 cm⁻¹), C—O (1050cm⁻¹), and C═O (1700 cm⁻¹). This observation is consistent with thehigher hydrophobicity observed for high moisture runs in thehydrophobicity chamber test. This indicated that steam generated duringdensification due to the available moisture could possibly act as areducing agent leading to the associated dehydration. 34 mm runsdemonstrate lower oxygen functionalities compared to 36 mm. This impliedthat possibly 34 mm runs generated higher steam temperatures due tohigher pressures than corresponding 36 mm runs and this helped indehydrating/deoxygenating the biomass to a greater extent. Aliphatic CH(2950 cm⁻¹) bonds were also reduced in the higher moisture runs due tothe reduction of weaker aliphatic carbon such as hemicellulose in thebiomass.

Summary of Examples 1-7

The results showed that a mixture of HTM and LTM biomass could bedensified without using any added binders. The added moisture to thefeed mixture gave the briquettes a waxy like coating and a shinyappearance due to the migration of lignin (entrained by steam frommoisture) from the interior of the briquettes. Also, it can enhancein-situ binding and thus increasing hydrophobicity and calorific value.At the same time, it can initiate cracks at the end product that reduceoverall density and durability. Higher density and durability wasrelated to the binding, higher briquetting pressure (i.e. using of 34 mmdie) and lower moisture content at the end product. Lightly torrefiedmaterial could be used as the source of natural binder (lignin) as theyprovide the chemistry and amount of lignin that is necessary forbinding. Briquettes of mixed torrefied levels of biomass with goodin-situ binding could give good heating value, hydrophobicity, densityand durability, and could be made in a large-scale production.

Introduction for Examples 8-9

In the following Examples, efforts were undertaken to hydrolyze biomassprior to torrefaction as a co-product strategy to improve economics ofbio-coal process. The added value of the xylose recovered fromhydrolyzate could offset the price of bio-coal production and becompetitive with current coal technologies. There is no prior study thatreports integration of pre-hydrolysis to extract and recoverhemicellulose-based sugars (e.g., xylose) and subsequent torrefaction ofhydrolyzed wood.

Materials and Methods for Examples 8-9

The wood chips used in the following Examples were obtained fromColeraine Labs Minnesota, Coleraine, Minn., United States of America.The wood chips were dried to less than 10 wt % moisture. Moisturebalance readings for each biomass were performed on 1 g samples using anIntelligent Weighing Technology Model IL-50.001 (Intelligent WeighingTechnologies, Camarillo, Calif., United States of America). Sulfuricacid used as a catalyst for hydrolysis reaction was purchased from VWR99% purity) (VWR, Radnor, Pa., United States of America) and was used asreceived.

In the study, dilute acid hydrolysis was conducted as describedpreviously for C5 sugar extraction. Acids strength of 4 wt % based onbiomass were maintained in the reaction. The hydrolysis reaction wasperformed in a 6 L M/K digester reactor with a ramp up time of 50 minand a reaction time of 1 hour at temperature of 140° C. and a pressureof 50 psi. 300 g of wood chips (dry weight) was used with 3 L of water.At the end of the reaction, the reactor was cooled below 40° C. byexternal water loop connected through a heat exchanger.

Hydrolyzate produced from the reaction was analyzed via HPLC (Water 600Eand Agilent 1260 Infinity, Agilent, Santa Clara, Calif., United Statesof America) for sugars and sugar degradation products. Resultingresidual wood chips were dried overnight in an oven at 60° C. to reducethe moisture content to less than 5 wt %. Both unhydrolyzed wood chipsand hydrolyzed wood chips were subjected to torrefaction treatment in atube furnace (MTI, GSL1500X, MTI, Richmond, Calif., United States ofAmerica) operating under nitrogen flow of 100 ml/minute. The temperatureof the furnace was maintained at 300° C. for 30 min with a temperatureramp-up time of 10° C./min. Sample weights after torrefaction wererecorded for both samples and they were subjected to moisture tests asdetailed above. The calorific value of the wood samples was measuredusing an IKA C2000 calorie meter. The calorie meter was calibrated using1 g of benzoic tablets prior to testing. For the analysis, around 1 g ofsolid pieces were extracted from wood samples. Moisture uptake of thewood samples were analyzed in a humidity chamber (Fisher ScientificHumidity Chamber, 905) maintained at 90% humidity at 30° C. The woodsamples were dried in a vacuum oven at 60° C. for 24 hours and dryweights were recorded. The dried samples were placed in the humiditychamber for 24 hours and weighed afterwards. The change in weightindicated the ability to absorb moisture, which can be used as anindicator of the hydrophobicity of the wood.

The molecular level chemical changes that occurred in wood duringhydrolysis and torrefaction were analyzed using an ATR enabled FTIRspectrometer (Spectrum 100, PerkinElmer, Sheldon, Conn., United Statesof America) for pieces of the briquette. About 20 mg of powdered samplewas (<40 sieve) placed on top of the ATR crystal covering the wholecrystal. FTIR curves obtained were normalized to C═C peak at 1506 cm⁻¹assuming relatively unchanged aromatic ring count during the MWtreatment.

Thermal analyses were also performed on these samples on SDT Q600 toquantify the ash content of the samples. Around 10 mg of the sample wasplaced in the furnace operating under air (carrier gas) and temperaturewas raised until 700° C. using a heating rate of 50° C./min. The weightloss curves were recorded to quantify the ash as the residual weight.SEM images of unhydrolyzed and hydrolyzed wood samples were obtainedusing FEI TESCAN SEM 600 to understand the structural changes thatoccurred during hydrolysis.

Example 8 Acid Hydrolysis

As seen in Table 3, hydrolyzate of wood contained a significant amountof xylose (12 g/L) out of total sugar of 14.4 g/L. This very highselectivity (82.3%) for xylose was advantageous in reducing recoverycost as a platform chemical. Table 4 indicated that hydrolysis of woodslightly enhanced the energy content of the wood and this enhancementcould be due to the removal of oxygen rich hemicellulose in hydrolyzedwood compared to cellulose and lignin. Interestingly, the torrefied posthydrolyzed samples showed an increase energy content of 5.5% compared totorrefied untreated wood.

TABLE 3 Sugar Products in Wood Hydrolyzate Total Acid Xylose GlucoseArabinose Sugars Sugar 11.8 1.0 1.5 14.4 Concentration (g/L) SugarSelectivity (%) 82.3 7 10.7

To understand this dramatic energy enhancement, further analyses wereperformed as detailed below. As mentioned in the method section FTIRspectrums were normalized to the aromatic peak at 1505 cm⁻¹ assumingintact single ring aromatic rings that originates from lignin (FIG. 5).As expected the oxygen functionalities that include OH (3000 cm⁻¹), C—O(1100 cm⁻¹) and aliphatic C—H (2800 cm⁻¹, 1300-1400 cm⁻¹) dropdramatically in post hydrolyzed wood with the removal of oxygen richaliphatic hemicellulose. Both the torrefied samples (unhydrolyzed andhydrolyzed) showed similar trend of reduced oxygen functionalities anddecreased aliphatics. The C═O (1700 cm⁻¹) bonds increased significantlyfor torrefied samples that could be coming from dehydrogenatingaliphatic COH bonds. Interestingly, the aromatic C═C at 1600 cm⁻¹ thatpredominantly represent polyaromatics, increased dramatically fortorrefied samples. These could be most probably coming from thedehydration and dehydrogenation of carbohydrate fraction of biomass aslignin ring opening reactions that needed to form polyaromatics are notplausible in the reaction temperatures employed for torrefaction (300°C.). For torrefied samples aliphatic alkene (1650 cm⁻¹) functionalitieswere also dramatically increased with possible dehydrogenation reactionsin the carbohydrate fraction of biomass. Interestingly, the hydrolyzedsample had a significantly lower amount of these polyaromatics andalkenes supporting the notion that these originated from carbohydrates.These results clearly indicated that hydrolyzed wood generated lowersoot and fines with polyaromatic structure during torrefaction. It wasbelieved that that finding could be very useful in reducing the fines intorrefied biomass that provide a major obstacle for commercializingtorrefied and densified biomass as an alternative for coal.

TABLE 4 Physical Characteristics of Hydrolyzed and Torrefied WoodMoisture Moisture Content Heating Uptake Yield (% from Value (% from (%from Type dry wt.) (btu/lb) dry wt.) feed) Untreated 6.3 8570 16.6 —Wood Hydrolyzed 5.3 8656 12.8 — Wood Torrefied 4.7 9168 — 70.9 UntreatedWood Torrefied 4.3 9671 — 71.0 Hydrolyzed Wood

The TGA air combustion performed (FIG. 6) for untreated and hydrolyzedwood demonstrated that the untreated wood had significantly higher ashleft over (˜5 wt) after combustion compared to hydrolyzed wood (˜2.5wt). This drop of ash could be attributed to ash leaching during acidhydrolysis which worked as a wood purification step in addition to otheradvantages mentioned above. This ash reduction can be hugely beneficialfor torrefied biomass combustion process considering additionaloperational steps that has to be incorporated to remove ash. Moreover,as shown in FIG. 6, the results indicated that hydrolyzed wood completedthe combustion earlier than untreated wood (550° C. vs 600° C.)indicating superior combustion characteristics compared to untreatedwood potentially leading to reduced reduction time (increased productionrate) in the torrefaction reactor. In scanning electron microscopy (SEM)images, hydrolyzed wood samples showed considerable number of pores,which were absent from the unhydrolyzed wood samples. This enhancedporosity could be attributed to the dramatic calorific value increaseduring torrefaction, possibly due to enhanced heat and mass transferthat prevailed in hydrolyzed wood compared to unhydrolyzed wood.

Example 9 Cost Analysis

A techno-economic analysis was performed to compare the two scenarios ofproducing torrefied biomass briquettes with xylose extraction andwithout xylose extraction. The bases for this analysis are detailed inthe Table 5 shown below.

TABLE 5 Basis for Cost Calculations Factor Value Comment 1 MT of woodchips (green)  $80 50% Moisture 1 MT of torrefied wood pellets / $220briquettes 1 ton of xylose $2,000 Short ton ($1/lb) Torrefied wood yield70% (80% max) Xylose yield 20% (25% max) Operating costs 40% Of totalrevenue Plant capacity 100,000 Torrefied wood MT/y pellets/briquettes

Assuming $80/MT price for the green wood chips with a moisture contentof 50%, torrefaction increased the value of wood chips to a price of$220/MT. Xylose price was adopted from the whole sale market price.Torrefied wood yield and xylose yield were assumed at 70 wt % and 20 wt% of the feed. The operating cost was estimated to be 40% of the totalrevenue. For xylose extraction scenario, it was assumed that thehydrolyzed wood was at a moisture content of approximately 50%, which issame as the feed wood chips.

Table 6 shows the results of the cost calculation carried out for thesetwo scenarios. The estimated plant cost increased by $5,000,000 forxylose extracted scenario due to additional equipment necessary thatinclude hydrolyzer and xylose separation unit. Cost of wood chips wouldbe nearly $22.9 million for both cases. When the revenues were compared,xylose scenario generate $50 million more per annually mainly due to byproduct income of xylose which amount to $57 million. The torrefied woodincome increased by $2 million. The yield was 70% due to higher BTUassociated with torrefied xylose extracted wood. Operating costscalculated as 40% of revenue was comparably higher for with xylosescenario. Base case payback calculated for xylose scenario provided avalue of 0.8 years, compared to negative value obtained for unhydrolyzedscenario, where it is impossible to payback as revenue after feedstockand operating costs was negative. When the sensitivity of payback isanalyzed for different biomass feedstock costs, it is evident that it isonly possible to have positive payback value if the feedstock value islower than $40/ton, which is very unlikely.

TABLE 6 Cost Analysis Results Without Xylose With Xylose Plant cost(estimated) $15,000,000 $20,000,000 Cost of wood chips (green)$22,857,143 Revenue: $22,000,000 $79,771,429 Torrefied wood pellets /$22,000,000 $22,628,571 briquettes BTU of torrefied 9170 BTU/lb 9670BTU/lb Xylose $57,142,857 Operating costs  $8,800,000 $31,908,571Payback (years) (1.55) 0.80 Payback Cost of wood chips ($/ton) Withoutxylose With Xylose $20 2.00 0.47 $40 8.47 0.55 $60 (3.80) 0.65 $80(1.55) 0.8 

Summary of Examples 8-9

In the foregoing study, hydrolysis of wood was performed to extract C5sugars prior to torrefying residual wood to produce bio-coal. Woodhydrolyzate contained xylose at a concentration of at 11.8 g/L with avery high selectivity of 82%. Hydrolyzed wood showed a slight increasein calorific value compared to unhydrolyzed wood, but mostinterestingly, the caloric value increase was significant for torrefiedhydrolyzed wood compared to torrefied unhydrolyzed wood. According toFTIR analysis, both hydrolysis and torrefaction reduced the oxygenfunctionality indicating increased hydrophobicity. This observation wassupported by the lower moisture uptake in hydrolyzed wood compared tounhydrolyzed wood. SEM images showed significant porosity enhancementfor hydrolyzed wood samples. These results collectively demonstratedthat hydrolysis enhanced porosity and hydrophobicity and that thisfacilitated torrefaction in improving calorific value. The ash contentwas also reduced due to hydrolysis leaching and this providesconsiderable advantage in handling during combustion. Further, thepreliminary techno-economic analysis performed indicate that ourscenario can generate NPV significantly higher than untreated wood. Insummary, the study demonstrated that hydrolysis based C5 extraction ofwood can be employed as a pretreatment step that provides a significantvalue addition as C5 platform sugars, in addition to providing low ashand higher energy bio-coal product.

Additional Examples

Briquetter Trial

Machine: C.F. Nielsen BPU3200

Die configuration (diameter in mm): (42-36)(36-36)(36-36)(36-40)

Temperature: 250° C.

Material: Mixture of 20% HTM and 80% LTM

MC=14%, material was processed as received without pre-heating

Results:

1. The Trial was successful.

2. The produced briquettes expansion also was lower as compared to theones produced from LTM only.

3. Although the briquettes have small cracks, they did not divide intosmall pucks.

4. The binding in these briquettes was better because of the increasedmoisture content.

5. The water soaking test revealed that these briquettes were better inhydrophobicity.

6. 14% MC with 20% HTM was glossy.

Briquette Trial

Summary

1. Ran two trials using LTM and HTM mix.

2. Die configuration (diameter in mm): (42-36)(36-36)(36-36)(36-40)

3. Temperature: 250° C.

4A. Material: Mixture of (10 and 20%) HTM with (90 and 80%) LTMMC=9.55%, material was processed as received without pre-heating

4B. Material: Mixture of 20% HTM and 80% LTM MC=14%, material wasprocessed as received without pre-heating

5. These trials showed that an increase in moisture significantlyimproved hardness as well as hydrophobicity for 80:20 mix of LTM andHTM.

6. The produced briquettes expansion also was lower as compared to theones produced from LTM only.

7. Although the briquettes have small cracks, the briquettes did notbreakup into small pucks.

8. It appears that the binding in these briquettes was better because ofthe increased moisture content and some preheating

9. The water soaking test revealed that the briquettes from trial stayedintact after 48 hours of soaking. This appears to show that thesebriquettes have acceptable level of hydrophobicity.

Briquetter Trial

1. Machine: C.F. Nielsen BPU 3200

2. Die configuration (diameter in mm): (42-36)(36-36)(36-36)(36-40)

3. Die Preheat Temperature: 250° C.; Die Operating Temperature: 220° C.

4. Material: Mixture of 20% HTM and 80% LTM MC=10.28%, material waspre-heated to about 50° C.

Results:

1. The produced briquettes showed good packing density, smoothformation, less cracks, and showed better binding (the briquettes didnot divide into small pucks) compared to other runs.

2. Radial expansion (diameter around 37 mm) of the finished briquettewas lower as compared to the ones produced from LTM only.

3. Similar to other trials, the briquettes showed good hydrophobicity,as no changes in the integrity of the briquette were observed even after72 hours of water soaking.

4. The briquette gained weight after 24 hours of water soaking. Theweight increased from 48 gm to 66 gm. Also, the sample diameterincreased 37 mm to 40 mm. The fact that the briquette is staying intactafter 72 hours and it is possible to pick it up from water confirms thathydrophobic bonding is being promoted in the briquette.

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference,including the references set forth in the following list:

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It will be understood that various details of the presently disclosedsubject matter can be changed without departing from the scope of thesubject matter disclosed herein. Furthermore, the foregoing descriptionis for the purpose of illustration only, and not for the purpose oflimitation.

1. A torrefied biomass briquette, comprising: (a) about 10% to about 95%of a highly-torrefied material (HTM) and about 5% to about 90% of alightly torrefied material (LTM); (b) a torrefied acid hydrolyzedbiomass having a FTIR profile comprising one or more reduced oxygenfunctionalities as compared to biomass not subjected to acid hydrolysis;or (c) a combination of (a) and (b).
 2. The briquette of claim 1,wherein, prior to densification, the HTM and the LTM have a combinedmoisture content of about 7% to about 15%.
 3. The briquette of claim 1,wherein, subsequent to densification, the briquette has a moisturecontent of about 3% to about 10%.
 4. The briquette of claim 1, whereinthe briquette exhibits lignin based in-situ binding and is free of anadded binder.
 5. The briquette of claim 1, wherein the briquette has adensity in the range of about 1 to about 1.5 gm/cm³.
 6. The briquette ofclaim 1, wherein the briquette has a durability index value of about 5%to more than about 90%.
 7. The briquette of claim 1, whereinhydrophobicity of the briquette is increased relative to a briquetteincluding only LTM.
 8. The briquette of claim 1, wherein the briquettehas a calorific value of about 8,000 BTU/lb to about 10,000 BTU/lb.
 9. Amethod of producing a torrefied biomass briquette, comprising: producinga mixture comprising about 10% to about 95% of a highly-torrefiedmaterial (HTM) and about 5% to about 90% of a lightly torrefied material(LTM); preheating the mixture to a predetermined temperature;compressing and simultaneously heating the mixture
 10. The method ofclaim 9, wherein, prior to the compressing and heating, the HTM and theLTM have a combined moisture content of about 7% to about 15%.
 11. Themethod of claim 9, wherein, subsequent to the compressing and heating,the briquette has a moisture content of about 3% to about 10%.
 12. Themethod of claim 9, wherein the mixture is pre-heated to a temperature ofabout 40° C. to about 80° C.
 13. The method of claim 9, furthercomprising the step of adjusting the moisture content of the mixtureprior to compression.
 14. The method of claim 9, wherein heating themixture comprises heating the mixture in a die to a temperature of about200° C. to about 250° C.
 15. The method of claim 9, wherein the mixturedoes not include a binder.
 16. The method of claim 9, wherein the LTMand/or the HTM of the mixture is formed by providing a biomass; andsubjecting that biomass to an acid hydrolysis.
 17. A torrefied biomassbriquette produced by the method of claim
 9. 18. A method of producing atorrefied biomass, comprising: providing an amount of a biomass;subjecting the biomass to an acid hydrolysis to produce a hydrolyzedbiomass; and torrefying the hydrolyzed biomass.
 19. The method of claim18, wherein the biomass comprises wood.
 20. The method of claim 18,further comprising the step of drying the biomass prior to torrefyingthe hydrolyzed biomass.
 21. The method of claim 18, wherein a portion ofthe hydrolyzed biomass is subjected to torrefaction at a temperatureranging from about 160° C. to about 220° C. and/or a portion of thehydrolyzed material is torrefied at temperatures above about 240° C. 22.The method of claim 18, further comprising compressing the hydrolyzedbiomass; and simultaneously heating the hydrolyzed biomass at apredetermined temperature to form a torrefied biomass briquette.
 23. Atorrefied biomass produced by the method of claim
 18. 24. A torrefiedbiomass briquette produced by the method of claim
 22. 25. The briquetteof claim 1, wherein the LTM is a hydrolyzed biomass.
 26. A biomassbriquette, comprising an acid hydrolyzed biomass having a FTIR profilecomprising one or more reduced oxygen functionalities as compared tobiomass not subjected to acid hydrolysis.
 27. The briquette of claim 26,wherein the briquette exhibits lignin based in-situ binding and is freeof an added binder.